MMR vaccine ‘does not cause autism’

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Behind the Headlines

Tuesday February 5 2008

The first MMR vaccination is given at 13 months

There is no evidence for a link between the MMR jab and autism, say The Guardian and other news sources. The reports are based on a study that is the “biggest review conducted to date”, analysing “the blood from 250 children and concluded that the vaccine could not be responsible”.

The jab has been linked to autism since 1998, when a study of 12 children published in The Lancet linked the measles, mumps and rubella (MMR) jab to the development of autism. That research has since been discredited and two major studies have been published subsequently which also failed to show any link.

In this latest UK study, researchers investigated whether the MMR vaccine contributes to the development of autistic spectrum. This study investigates some of the specific suggestions that have been put forward about the relationship between the MMR vaccine and autistic spectrum disorders in the past. These include the idea that the MMR vaccine was specifically associated with autism where children experienced a loss of developed skills (regression) and inflammation of the small intestine (enterocolitis); that autism is associated with an increased level of measles antibodies in the bloodstream; and that it's associated with an increased presence of genetic material from the measles virus in cells from the gut.

The researchers looked at three groups of children, one with autistic spectrum disorders, one with special educational needs but no autism and another who were developing normally. When blood samples were compared, there was no difference in any long-lasting signs of measles virus or increased levels of antibodies to the measles virus between the groups. They also found that enterocolitis was not commonly associated with autism. This study adds to the pool of evidence that suggests that there is no causal link between the MMR vaccine and autism.

Where did the story come from?

Professor Gillian Baird and colleagues from Guy’s & St Thomas’ NHS Foundation Trust, several Universities in the UK and Australia, the National Institute for Biological Standards and Control and the Health Protection Agency in the UK carried out this research. The study was funded by the Department of Health, the Wellcome Trust, the National Alliance for Autism Research, and Remedi. The sponsors did not play a role in study design, data collection, analysis or interpretation, or in writing the paper. It was published in the peer-reviewed medical journal: Archives of Disease in Childhood.

What kind of scientific study was this?

This was a case-control study which tested the possibility that the MMR vaccine may contribute to the development of autistic spectrum disorders (ASD). The researchers did this by comparing long-lasting signs of measles infection or immune response in children with ASD (cases) and children without ASD (controls). The researchers were particularly interested in looking at children who had lost some of their developmental skills (called regression) and children with specific digestive system problems (enterocolitis), as these are both phenomena that have been claimed to be linked to the MMR vaccine. This study was part of the Special Needs and Autism Project (SNAP), which enrolled 56,946 children from the South Thames region born between July 1 1990 and December 31 1991.

No association between measles vaccination and ASD was shown.

Gillian Baird, lead author

There were 1,770 children from SNAP aged nine to 10-years-old, who had been classified as having special educational needs or had been diagnosed with ASD. A representative sample of 255 of these children were selected to have a standard in-depth diagnostic test for ASD. For this study, the researchers included only children who provided blood samples, and those who had received the MMR vaccine at least once. Information about whether a child had had the MMR vaccine was taken from parental report, GP and district records. This included 98 children (cases) with ASD and 52 children with special educational needs but not ASD (controls). They also selected another control group of 90 children from mainstream local schools who were developing normally, had received the MMR vaccine, and had agreed to have blood taken. All the children were aged between 10 and 12. The people who tested the blood samples did not know which were from cases and which from controls.

The researchers looked to see whether there were antibodies against the measles virus in the blood and investigated whether the levels of anti-measles antibodies a child had was related to the severity of their autistic symptoms. The children’s blood samples were also tested for the presence of the measles virus by looking for genetic material from the virus. Previous studies have looked for the measles virus in cells from the stomach, however, as this is an invasive procedure it was considered unethical to carry out this procedure on the children, so instead the researchers looked at a particular type of white blood cell where viruses are known to replicate.

The researchers also asked the children’s parents or guardian to complete a questionnaire about whether the children had symptoms of digestive system problems either in the past three months (current symptoms) or before (past symptoms). Children with persistent diarrhoea in the past, who did not have current constipation, and who had two or more of the following current symptoms were defined as having “possible enterocolitis”: persistent vomiting, persistent diarrhoea, weight loss, persistent abdominal pain, or blood in stool.

The analyses were repeated to see whether their results differed in children who had received one compared with two doses of the MMR vaccine, or in children who had ASD with regression (defined as loss of five or more words in a three month period) compared with those with ASD but without regression.

What were the results of the study?

There was also no difference in the level of antibodies to measles in the bloodstream between children with ASD (cases) and children without ASD (controls). Also, there was no relationship between the level of measles antibodies a child had and how severe their autistic symptoms were. For the 23 children with ASD and regression, there was also no difference in the levels of antibodies between them and the pooled control group.

Genetic material from the measles virus was only found in one child with autism and two children who were developing normally. However, when they repeated the tests, the researchers could not find any measles virus genetic material in these samples.

Only one child had symptoms which could indicate enterocolitis, and this child was in the control group.

What interpretations did the researchers draw from these results?

The researchers concluded that there was no link between the MMR vaccine and autistic spectrum disorders.

What does the NHS Knowledge Service make of this study?

This study selected cases and controls from a large community based group, and the researchers tried to include all the children with ASD in this community. The limitations of this study were acknowledged by the authors and included the fact that:

The children were not randomly selected from the population. This may mean that the samples may not truly represent the groups of children that they were meant to represent (that is, children with ASD, children with special educational needs, or developmentally normal children).

The researchers could not obtain adequate blood samples from 100 children. If these children differed systematically from the children from whom blood samples were obtained, this could affect results.

The diagnosis of “possible colitis” was based mainly on current symptoms, because it was thought that it would not be possible for the parent or guardian or child to accurately recall whether the child had experienced these symptoms at the time of having the MMR vaccination (more than nine years previously).

This study adds to the pool of evidence that suggests that there is no causal link between the MMR vaccine and autism.